Image credit: Johan Cedervall, 2017. CC BY-SA IGO 3.0. This material is a strong magnet investigated for the use in wind power plants and other applications.
Almost everyone has seen magnets in action when sticking a birthday card or the drawing of a child to a refrigerator. Some might have even used one when taking a compass on a hike. There is one more important application for magnets that most of us have seen: wind power plants. The generators inside wind power plants use very strong magnets to create electricity. These magnets are normally made from the elements neodymium, iron and boron.
While iron and boron are are relatively easy to extract and separate from their minerals (or stones), neodymium is a rare-earth element. There are in total 17 rare-earth elements and despite their name, they are actually quite plentiful in the Earth`s crust. The problem is that these elements tend to occur together in the same minerals which makes their extraction and separation extremely difficult and expensive. In addition, China stands for 85 % of all rare-earth element production which provides a monopoly position enabling it to dictate prices and make other countries dependent. Besides, there are strong environmental as well as health and safety concerns about the mining procedures used in China.
For these reasons research is carried out to find new neodymium-free or rare-earth-free, strong magnets. I have spoken to Johan Cedervall, a PhD student in the Inorganic Chemistry group at Uppsala University, who is trying to make new rare-earth-free magnets for wind power plants and other applications. Cedervall is working on magnetic materials composed of iron, boron, phosphorus and silicon, all abundant materials which are relatively easy to extract from their minerals.
To produce his magnets, Cedervall melts the elements together in an electric arc (basically a permanent, artificial lightning) at 1500 to 2000 °C (2732 to 3632 °F) under argon atmosphere. This procedure results in a highly magnetic, grey compound as seen in the image above. According to Cedervall, his materials are generally a bit less magnetic and easier to demagnetize than conventional neodymium-based magnets, which is a disadvantage. But they are also much cheaper thanks to the absence of neodymium.
Nevertheless, Cedervall says, that the goal is to find even stronger rare-earth-free magnets than his for the use in wind power plants. The problem is that weaker magntic materials have to be used in larger amounts to reach the effect of a neodymium-based compound. For this reason, the search for strong, rare-earth-free magnets is ongoing.
Cedervall believes, that we will see a shift to rare-earth-free or rare-earth-lean (containing smaller amounts of neodymium) magnets in the near future. Wind power plants are being built at a rapid pace all over the world at the moment. To maintain this development, industry will sooner or later be forced to turn to alternative magnets. The German company Enercon has, in fact, already implemented neodymium-free technology into their wind turbines. In addition, magnetic materials called ferrites, for example strontium iron oxide, have already started to replace neodymium in other applications.
When asked which results of his research he is most proud off, Cedervall answers, that these are actually not related to wind power plants. All magnets lose their magnetic properties at a certain temperature when they are heated. This point is called Curie temperature which is between 500 and 600 °C (932 and 1112 °F) for Cedervall`s materials. He has found that this point can be tuned by the gradual substitution of iron with cobalt. A higher cobalt content decreases the Curie temperature, while a lower one increases it. This result could be interesting for building magnetic refrigerators that are safer and more environmentally friendly. The details of this application are a story for another time.
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Most wind turbines didn’t use permanent (rare earth) magnets until relatively recently, instead using a conventional gearbox. Several companies have moved to direct-drive technology, abandoning the gearbox. Here is where the permanent magnets come in – or Enercon’s alternative which you linked to. Permanent magnets do make turbines operate more efficiently, but they are certainly not essential to wind energy technology.
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